The Development Of The Mercedes-Benz A-Class: The Diesel Engines - Economy Right Across The Board

Downsizing for the entry-level engines and downspeeding for the more powerful units - that is the Mercedes-Benz strategy for the diesel engines in the new A-Class. The wide range meets every performance requirement, and demonstrates the potential residing in the diesel engine: for the first time - with the A 180 CDI - a Mercedes-Benz will emit just 98 g of CO2 per kilometre. The diesel engines also boast extreme efficiency and environmental friendliness, thanks to state-of-the-art injection technology and turbocharging. The A 180 CDI kicks off at 80 kW (109 hp) and offers maximum torque of up to 250 Nm (dual clutch transmission) or 260 Nm (6-speed manual transmission). In the A 200 CDI the maximum power output stands at 100 kW (136 hp), accompanied by maximum torque of 300 Nm. The A 220 CDI has a displacement of 2.2 litres and generates 125 kW (170 hp) with 350 Nm of torque, giving the performance of the A-Class a decidedly sporty touch.

Since its world premiere in 2008 the direct-injection diesel engine known as the OM 651 has been setting standards in terms of performance and torque characteristics, economy, emissions and smooth running. It is in more widespread use than any other Mercedes-Benz diesel engine and serves as a model of efficiency and power right up to the S-Class. For transverse installation the belt drive for the ancillary units, the installed position of the turbocharger and the air ducting have been modified. Dynamic to drive, extremely efficient and outstandingly clean, the A 220 CDI is only available in combination with the 7G-DCT dual clutch transmission. The 1.8-litre engine variant is used in the A 180 CDI with the 7G-DCT dual clutch transmission and the A 200 CDI. The displacement was reduced by shortening the stroke (83 mm instead of 99 mm). The significantly longer connecting rods ensure lower transverse friction, and the two Lanchester balancer shafts are also of low-friction design.

The single-stage turbocharger was optimised for efficiency and features adjustable vanes. With a distance between cylinders of 94 millimetres and cylindrical gears driving the camshafts, transverse installation and the necessary length restriction were part of the design specification from the very start. To realise the start/stop function, the belt drive is decoupled from the crankshaft in all three engines. Common rail technology with a rail pressure increased to 1800 bar. The maximum ignition pressure of 180 bar also contributes to the high power output and a muscular torque curve. The oil injection nozzles and the water pump are activated only when required, in order to save energy and fuel. The controlled oil pump additionally reduces oil flow and thus fuel consumption. The engine block is made of cast iron, the cylinder head of aluminium. A two-piece water jacket in the cylinder head provides for optimum cooling in the area of the combustion chamber plate.

This enables an ignition pressure of 200 bar and a high specific power output. The cast iron barrels have undergone considerably finer honing than on the predecessor, also contributing to the reduction in fuel consumption. To compensate for the second-order forces which are inherent to four-cylinder in-line engines there are two Lanchester balancer shafts at the bottom of the engine block running in low-friction roller bearings rather than conventional plain bearings. The two-mass flywheel has been specifically designed for high engine torque at low engine speeds in order to isolate the crankshaft's vibration stimuli, thereby contributing to the engine's excellent smooth running. For the A 180 CDI with manual transmission Mercedes-Benz has had recourse to its cooperation with Renault to achieve fuel economy advantages from a compact, lightweight, low-friction engine which has been rigorously downsized. The common-rail four-cylinder with a rail pressure of 1600 bar is currently in its sixth generation, with more than 1.3 million units produced each year.